Before all the planets migrated in our solar system, it looked very different. The solar system was filled with a large, donut-shaped cloud of gas and dust called the protoplanetary disk. The disk extended far beyond the orbit of Pluto and was made up mostly of hydrogen and helium, with small amounts of other elements such as oxygen, carbon, and nitrogen.

In the center of the protoplanetary disk was the young sun, which was still forming and growing in size. The solar nebula was heated by the sun's radiation, and as it cooled, it began to form small clumps of matter called planetesimals.

Over time, the planetesimals grew in size by colliding and sticking together, eventually forming the planets and moons that we see in the solar system today. The inner planets, Mercury, Venus, Earth, and Mars, were formed first, followed by the outer planets, Jupiter, Saturn, Uranus, and Neptune.

As the planets formed, they began to interact with each other gravitationally. This interaction caused the planets to move around in their orbits, and eventually led to the formation of the stable planetary system that we see today.